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三田図書館・情報学会誌論文(論文ID LIS023137)

Weighted Document Retrieval Systems Based on Fuzzy Set Theory Approaches
No.23, p.137-147

There exist unavoidable drawbacks in the conventional document retrieval systems based on Boolean logic. Every keyword assigned to the documents in the collection is given equal weight irrespective of its actual relatedness to each document. This aspect is also applicable to the search formula where keywords are treated equally, and there is no chance for a searcher to specify the extent of the keyword’s significance. In addition, AND operators are excessively influential when narrowing the range of the documents to be retrieved.

In order to get rid of the defects, a variety of techniques have been introduced into retrieval systems such as models using conditional probability theory, vector space, and so forth. Fuzzy set theory approaches are among these and are quite promising for this purpose since human behavior is essentially so fuzzy that it is difficult to be represented by, for example, probability terms.

This paper describes following items concerning fuzzy retrieval systems from this viewpoint.

1) General characteristics of fuzzy retrieval

2) Roles and functions of the weight

3) Calculation formula for the ‘Retrieval Status Value’

4) Manipulating methods of the metamorphic functions of Boolean logical operators

Finally, this paper mentions some problems of determining legitimate RSV and e1 formula, especially for handling NOT function, and of selecting adequate Membership Functions, when developing operational fuzzy retrieval systems.

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